The present invention relates to the reduction of noxious exhaust gas components discharged at the time of starting a cylinder injection type internal combustion engine in which fuel is injected directly into the combustion chamber by means of the fuel injectors.
Hydrocarbon (HC) as unburned fuel is one of the noxious exhaust gas components discharged at the time of starting a cylinder injection type internal combustion engine. During the warming-up period of an internal combustion engine which follows the start-up of the engine, the three-way catalyst for purifying the HC left as unburned fuel is not yet activated. Thus, the HC to be discharged out of the engine cannot be purified and the unpurified noxious substance is discharged into the air. It is therefore required that HC discharged from an internal combustion engine should be reduced at the time of starting the engine. The cause of HC being discharged out of a cylinder injection type internal combustion engine in cold starting, may be ascribed to unburned fuel adhering to the internal surface of the cylinder and/or the top surface of the piston head. Namely, in cold state of the cylinder injection type internal combustion engine, the direct injection of fuel into the cylinder may causes the adhesion of fuel onto the surface of the cylinder or piston head. While the engine is still cool, the adhering fuel cannot be vaporized and may be discharged as unburned fuel that is noxious HC.
JP-A-2000-8915 discloses a technique which takes the above described situation into consideration. According to the technique, the inflow of air sucked into the combustion chamber is enhanced and the air flow strong enough is created in the chamber, by controlling the timing of opening the intake valves and the timing of fuel injection and further by reducing the lift amount (valve opening) of the intake valves, so that the adhesion of fuel onto the surface of the cylinder or piston head can be suppressed with the result that the amount of HC discharged out of the engine is reduced.